Certain 3,3′-azo-bis(6-hydroxybenzoic acid) derivatives have useful properties and can be used as pharmaceuticals or dyestuffs. One such compound, the disodium salt of 3,3′-azo-bis(6-hydroxybenzoic acid) 1 [disodium olsalazine 1d] is marketed as a pharmaceutical for the treatment of ulcerative colitis under the trade name Dipentum®.
Processes for the preparation of 3,3′-azo-bis(6-hydroxybenzoic acid) 1 and its salts and derivatives are known and have been disclosed in patents EP 0036636 and DD 276863.
The inventors of the present application have developed a process, particularly useful for industrial scale manufacture, as it is short, simple and high yielding. The process does not use any hazardous or difficult to handle reagents and is an improvement on currently known processes for the industrial scale manufacture of 3,3′-azo-bis(6-hydroxybenzoic acid) 1 and its salts and derivatives.